Texture brush doesn't make clear or smooth geometry on sculpture
These so-called Alpha brushes require a very high polycount to look good. I've done some tests with the Lips Alpha brushes by Todor. You can get the Light version here for free (https://gumroad.com/l/lipsfree) if you want to try it out yourself. It comes with a short manual for the brush settings.
The following images show the included example blend. The lips are low-poly with a Multires modifier, with 3, 4, and 5 subdivisions. 6 subdivisions (=2.4 million vertices) show no improvement in comparison to 5 subdivs.
If you have a fully sculpted character or creature you will end up easily with a few million verts like in this video: Create High Resolution Sculptings in Blender (24 million verts)
If your PC can't handle such a high amount of verts you can use a Bump Map and paint the details on a texture as shown here: Node Based Texture Painting in Blender 2 8
Hope that helps :-)